Process of manufacturing fibers of polyethylene terephthalate



April 26, 1960 slGGEL ETAL PRQCESS OF MANUFACTURING FIBERS OF POLYETHYLENE TEREPHTHALATE Flled March 19 1956 INVENTORS:

5 WW L T EA M GR G w C A WM .L MR RA EK PROCESS OF MANUFACTURING FIBERS OF POLYETHYLENE TEREPHTHALATE Erhard Siggel, Laudenbach (Main), and Karl Macura, Klingenberg (Main), Germany, assignors to Vereinigte Glanzstofi-Fabriken A.G., Wuppertal-Elherfeld, Germany This invention relates to a process of manufacturing fibers of polyethylene terephthalate, and is particularly applicable to manufacturing staple fibers of polyethylene terephthalate.

Where a staple fiber is to be manufactured from a polyamide,. filaments of the polyamide twisted into a continuous cable are progressively stretched at increased temperature, Washed and subsequently dried, and then crimped at an increased temperature, after which the cable is cut into staple lengths. Another process for manufacturing staple fibers, which is applicable to regenerated cellulose or polyamides, strongly twists the freshly spun, still plastic. threads so that the resulting twist can be fixed by washing, steaming, etc., followed by an untwisting and subsequent cutting of'the cable or filaments into staple lengths. In another process, particularly applicable to polyamides, the polyamide filaments are stretched at an elevated temperature, cooled while-still under tension in a gas or air current or by spraying with water, then cut into staple lengths, after whichthe cut fibers are treated with hot water to produce-a crimped characteristic in the staple fiber.

These known processes, such as those applied to polyamide fibers, are generally not suitable for application to polyethylene; terephthalate fibers. Various problems arise in the manufacture of polyethylene terephthalate fibers particularly for. the reason that these fibers absorb. considerably less Water moisture than do polyamide, polyacrylic nitrile, regenerated cellulose and other synthetic fibers. .The water or moisture content of a spun polyethylene terephthalate filament, for instance, does not usually exceed 1%, whereas, in coutrast, polyamide filaments. have a moisture content-which amounts to about 4%. terephthalate filaments has been found to present a particular problem in. that step of theprocess wherein a-freshly spun or nomoriented fiber is stretched. in the presence of steam to, obtainan oriented fiber. Where polyethylene terephthalate filaments are collected in the form of a, cable and passed into a steam atmosphere, water drops collect or condense at individual'points along the cold cable. At those local points which are excessively loaded with drops of water, heat transfer to the cable is inferior with the result that the cable is insufficiently stretched or not stretched at all at these points. On the other hand, the portions of the cable where water drops have not condensed exhibit a very low moisture content so that heat penetrates the fiber quite rapidly and permits the fiber to stretch easily. As a result, the local. water condensation and non-uniform heating of thecable produces filaments which are stretched differently at different portions of the cable or, in other words, produces filaments which have a non-uniform crosssection.

. When such non-uniformly stretched filaments are dyed, that unstretched portions of greater cross-section take considerably, darken shades; of. color; than do thestretched The low moisture content of polyethylene Patented Apr; 26, 1960 portions because of the absorption of a greater amountof pigment. Physical properties such astensile strength, e.g., will also vary in an unevenly stretched filament; Another difficulty which arises because of local water condensation on the cable is that those portions of the cable having a low moisture content become overheated to such an extent that the not fully stretched polyethylene terephthalate filament becomes thermoplastic as it passes through the steam zone. The filaments then tend to stick together or to break because of friction betweenindividual filaments in stretching. Such overheating is particularly troublesome when it exceeds C. In extreme cases, excess heat will cause thermal decomposietion of the unstretched polyester.

One object of this invention is to provide a process of manufacturing fibers of polyethylene terephthalate in' which the individual filaments are uniformly stretched to give a substantially uniform. cross-section and also tensile strength.

Another object of the invention is to provide. a process. 7

of manufacturing fibers of polyethylene terephthalate in which the filaments can be uniformly heated during' stretching, thereby overcoming the various difficulties discussed above, including filament breakage, damage,- decomposition, and the like.

Still another object of the invention is to provide a process of manufacturing fibers of polyethylene terephthalate which will result in staple fibers having a substantially uniform cross-section and capable of being dyed with a uniform shade of color.

These and other objects and advantages of theinvention will become more apparent upon a consideration of the detailed description which appears hereinafter.

In accordance with the invention, it has now been found that fibers of polyethylene terephthalate can be manufactured in an advantageous manner by the in corporation of particular steps into the usualprocess for producing such fiber. Thus, in the usual process, a plurality of continuous filaments of polyethylene terep thalate are spun and collected into a continuous cable, tow, strand, yarn, bundle or the like and then stretched for orientation of the fibers in the presence of a steam stretching step is particularly useful when taken in combination with subsequent steps for the production of a staple fiber of polyethylene terephthalate. A staple fiber, product having highly uniform qualities is thusobtained by a process which includes spinning a plurality of continuous filaments of polyethylene terephthalate from the melt, collecting these filaments into a continuous tow,, applying a uniform moisture content on the tow of from. 4-lO% by weight of dry cable, stretching the. tow with. this moisture content in the presence of steam. for. fiber. orientation, washing the stretched tow in a hot aqueous: bath under tension to remove adherent spin finish, and; to provide shrink resistance in subsequent steps, subjects ing the tow to a finishing treatment in which the filaments. are given a thermally insulative coating, crimping; the: filaments of the tow, drying the tow having crimpedfilaments in the absence of tension, subjecting the dried, tow to at least two tension steps providing successively increasing tension to substantially detach individual filaintostaple lengths of fiber.

The inventive features of the new process are more clearly set forth by the following description of a process of manufacturing staple fibers wherein a continuous tow is cut into staple lengths. It is to be understood, however, that particular features of the invention are equally applicable to the production of continuous filaments of polyethylene terephthalate. The process for the production of staple fibers of polyethylene terephthalate begins With spinning a plurality of continuous filaments of polyethylene terephthalate from the melt. The spinning of the fibers or filaments is accomplished in the usual manner by extruding the molten polyester through a spinneret and solidifying the spun filaments. Generally, any number of filaments, e.g., from 300 to 200,000 filaments, can be spun at the same time and are collected together to form a tow of filaments. The filaments of the freshly spun polyester are non-oriented so that the tow has a low denier and high extensibility; e.g., the tow may be characterized as being from 300 filaments, 18,000 denier to 200,000 filaments, 1,104,000 denier. Y t

In order toorie-nt the fibers and provide greater tensile strength to the individual filaments, it is necessary to stretch or draw the tow under a stretching tension to several times its length. As noted above, this stretching step can be accomplished in a much improved manner according to the invention by applying a uniform water moisture content to the tow of from 440% by weight of dry tow. The necessary quantity of water is applied before the tow enters into the steam atmosphere of the stretching zone, preferably by spraying water through a suitable nozzle or the like onto the tow. A greater amount of water than l% by weight of dr tow is to be avoided, and, therefore, the quantity of water applied to and absorbed by the tow must be carefully controlled. The quantity of water required for spraying on the tow naturally depends on the speed of the tow as it passes through the spray and also upon its thickness. Ordinarily, water should not be applied to the tow by passing the tow through a water bath since this method of application is not easily controlled.

Spraying water on the tow essentially results in the application of a uniform water jacket along the length of the tow. As the tow enters into the steam zone, the absorbed moisture content protects the unstretched tow against overheating and a tendency to become thermoplastic. The uniform moisture content also promotes an even or uniform heating of the individual filaments so I at a uniform stretching can take place. Furthermore, broken or damaged filaments are prevented since the individual filaments do not tend to become thermoplastic.

The tension required for drawing or stretching the tow is ordinarily accomplished in the usual manner by a set of rollers, including feed rollers placed before the steam zone and draw rollers placed after the steam zone. The feed rollers also act to homogenize or un formly equalize the moisture content in the tow as it passes over these rollers. It is also possible to provide a separate set of rollers prior to the steam zone in order to ensure an equally distributed moisture content in the tow.

In the stretching zone, the tow can be stretched from 3.5 to 5.5 times its original length and is usually stretched about four times its length. For the production of staple fibers the tow is ordinarily stretched less than a tow which is intended for use as continuousfilament fibers. Thus, a tow having from 600 filaments, 6300 denier to 100,000 filaments, 1,650,000 denier, can be stretched from 3.5 to 5.5 times its original length to produce a tow having from 600 filaments, 1800 denier to 100,000 filaments, 300,000 denier.

After stretching, the tow should contain a water moisture content of more than 0.5 and preferably more than 2%. The tow then passes in continuous operation into a hot aqueous bath, preferably maintained at a temperature of from about 60 to 90 C. Spin finish which still adheres to the tow is removed in the aqueous bath. It has been found to be highly advantageous to subject the tow to a definite tension during washing in the hot aqueous bath, sufiicient tension being applied to prevent shrinkage caused by increased temperatures in subsequent steps of the process. Also, if the tow is passed through this bath without the application of tension, high shrinkage tends to occur in the bath itself resulting in uncontrolled changes in the physical characteristics and particularly .in the cross-sectional area of the filaments. The tension applied to the tow in the bath is particularly important in preventing shrinkage in a subsequent crimping step which is especially accompanied by an increase in temperature. Generally, a tension of from about 0.5 g./den. to 2 g./den. is sufiicient to prevent shrinkage in a subsequent crimping step, the amount of tension naturally depending upon the size and number of filaments.

After washing and prior to crimping, the tow is subjected to a finishing treatment in which the filaments are given a thermally insulating coating in order to avoid overheating the filaments with resulting thread damage in the crimping operation. The finishing treatment for this purpose is Well known in the art and can be accomplished, e.g., by passing the tow through a bath of such finishing materials as polyethylene glycolester of high molecular fatty acids. Other finishing agents may also be applied to the tow during this stage of the process for various purposes as are well known in the art.

After the application of the finishing agents, the tow is crimped so that the individual filaments have a wavy, crinkled, or bent configuration. Various methods of crimping polyethylene terephthalate fibers are well known in the art and any suitable method may be employed, e.g., by passing the tow througha series of rollers which bend the fibers at short intervals along their length.

The crimped tow is then' dried in the absence of tension to a moisture content of about 0.5% and preferably less than 0.5%. The finishing agents previously applied to the tow cause the individual filaments to stick or adhere together. If the tow were immediately cut into staple lengths (as has been the customary procedure prior to this invention), it would then be necessary to subject the staple lengths of fiber after cutting to an additional opening operation before the staple fibers could be used in many textile applications. A highly advantageous feature of the present invention resides in subjecting the dried tow to at least two tension steps prior to cutting the tow into staple lengths. These tension steps cause the individual filaments to separate or detach from each other due to the resilience of the crimped fibers. Successively increased tension is applied in each step in order to prevent too high a tension from resulting in broken filaments. For example, where two tension steps are employed, the lighter preliminary tension can be applied by any suitable means such as braking the tow as it changes its direction of travel over rigid rollers spaced about four meters apart so that the tension lasts about /2 second. A second increased tension is then applied, preferably by means of a pair of rollers which operate at a slower speed than the feed mechanism for the cutting operation. This second tension also lasts for a short length of time, and is constant for a continuous tow having uniform characteristics. It is preferable to provide suitable means for adjusting the tension in order to accommodate tows and filaments of various sizes or thickness and other characteristics. The amount of tension applied should be suflicient to detach the individual filaments from each other, depending upon the desired opening of the resulting fleece. At the same time, the detached filaments should hang together well in spite of their separation, the crimped nature of the filaments aiding in this function.

After the tension steps, the loosely associated filaments are cut into staple lengths, e.g., from 3.1 cm. to 12 cm., by. any suitable cuttingmechanism. The resulting staple spinning to cutting into staple fibers, and

Fig. 2 is a perspective diagrammatic view of the watercoated filaments of the tow in the steam atmosphere of the stretching zone 4.

Example Polyethylene terephthalate is melted and spun through a 250 hole spinneret 1 according to common processes. The filaments were collected into a continuous tow 2 of 54,000 filaments. The tow has a titre of about 1,000,000 denier. This tow is loaded with a moisture content of 6% by weight of the dry tow by spraying with water from spray nozzles 3 and is then led into the stretching zone 4 in which a steam atmosphere is present (overheated steam of 130 (3.). Here the cable is stretched to 4.5 times its original length by means of feed rolls 5 and draw rolls 6 so that after the stretching-process has been finished the tow possesses a titre of about 162,000 denier. Fig. 2 of the drawing diagrammatically illustrates a segment of the tow in stretching zone 4 wherein the individual filaments 17 of the tow are stretched in the presence of an atmosphere of steam 19, while the filaments are coated with a film of water 18. The stretched tow, still under tension, is then led into an aqueous bath 7 which is heated to 85, to remove adherent spin liquor, subjected under tension to a finishing treatment at 70 C. The finishing bath 8 consists of a polyethylene glycol ester of high molecular fatty acids. Still under tension the tow is continuously led to a turbo-crimper 9 in order to be crimped and is then fixed under reduced tension in the presence of hot steam in zone 10. Now the tow is dried in zone 11 in the absence of tension, subjected to at least two short tension steps and led to the cutting apparatus for cutting it into staple lengths of 100 mm. fiber.

The first tension step is accomplished by running the tow zigzag through a series of staggered bars functioning as a brake 12 on the running tow. Ihe tow runs over a series of deflection rollers and a dancer roller 13 to a driven roller pair 14. The dancer roller 13 compensates for variations in tension imparted to the tow section running between brake 12 and the roller pair 14. The second tension step is provided by operating the clamping rollers 15 of the cutting device 16 at a higher drawing-off speed than the peripheral speed of the roller pair 14.

The invention is hereby claimed as follows:

1. In a process of manufacturing fibers of polyethylene terephthalate wherein a continuous tow containing a plurality of non-oriented filaments is stretchedin the presence of steam for fiber orientation, the improvement comprising applying a uniform coating of water to the tow of from 4 to 10% by weight of dry tow prior to stretching, said coating of water remaining upon said towduring stretching in the presence of steam.

2. In a process of manufacturing fibers of polyethylene terephthalate wherein a continuous tow containing a plurality of non-oriented filaments is stretched in the presence of steam for fiber orientation, the improvement comprising spraying sufficient water-on the tow to provide a uniform coating of Water of from 4 to 10% by weight of dry tow prior to stretching said coating of water remaining upon said tow during stretching in the presence of steam.

3. In a process of manufacturing fibers of polyethylene V terephthalate, the improvement which comprises spinning and then solidifying molten polyethylene terephthalate into a continuous tow of from 200 filaments, 18,000 denier, to 200,000 filaments, 1,104,000 denier, applying a uniform coating of water to the tow of from 4 to 10% by weight of dry tow prior to stretching, and subsequently stretching the substantially non-oriented filaments of the tow having said pre-applied coating of water in the presence of steam for fiber orientation.

4. An improved process as claimed in claim 3 wherein the filaments of the tow are stretched from about 3.5 to 5.5 times their original length.

5. An improved process as claimed in claim 3 wherein the stretched and oriented filaments are subsequently maintained under sufiicient tension and protected from excessive heat to avoid uncontrolled changes in the cross sectional area of the filaments.

References Cited in the file of this patent UNITED STATES PATENTS 2,332,485 ,Hanson Oct. 19, 1943 2,377,810 Robbins June 5, 1945 2,394,540 Finzel Feb. 12, 1946 2,395,396 Conaway Feb. 26, 1946 2,542,973 Abernethy Feb. 27, 1951 2,615,784 McClellan Oct. 28, 1952 2,733,122 Herele et a1. Jan. 31, 1956 2,734,794 Calton Feb. 14, 1956 

3. IN A PROCESS OF MANUFACTURING FIBERS OF POLYETHYLENE TEREPHTHALATE, THE IMPROVEMENT WHICH COMPRISES SPINNING AND THEN SOLIDIFYING MOLTEN POLYETHYLENE TEREPHTHALATE INTO A CONTINUOUS TOW OF FROM 200 FILAMENTS, 18000 DENIER, TO 200,000 FILAMENTS, 1,104,000 DENIER, APPLYING A UNIFORM COATING OF WATER TO THE TOW OF FROM 4 TO 10% BY WEIGHT OF DRY TOW PRIOR TO STRETCHING AND SUBSEQUENTLY STRETCHING THE SUBSTANTIALLY NON-ORIENTED FILAMENTS OF THE TOW HAVING SAID PRE-APPLIED COATING OF WATER IN THE PRESENCE OF STEAM FOR FIBER ORIENTATION. 